condorcet

Condorcet Library

A TypeScript library that implements various Condorcet voting algorithms.

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Ballots

The library exports a Ballot type, which is a Map of a key (which must be a string or a number, and which is also typed as Candidate) and a value (which must be a number). All the algorithms use this ballot. Typically, the magnitude of the ranks is irrelevant. All that matters is their sequence. For example, you could rank your first choice as 100 as long as your next choice was something like 110 and so on down the line. But this might differ by algorithm. Traditionally you indicate your first choice with a 1 and go from there. You do not need to vote for all candidates. Skipping a candidate simply means they're at the very bottom of your list.

Here's an example of a ballot ranking five candidates in the order ACBED:

const b: Ballot = new Map([
    ["A", 1],
    ["C", 2],
    ["B", 3],
    ["E", 4],
    ["D", 5]
]) as Ballot;

Available Algorithms

For all algorithms, the constructor takes the list of candidates, after which you can use the addBallot method. You can then call the rank method to get a list of candidates in order, winner first.

Schulze

A description of the method can be found on Wikipedia.

import { Candidate, Ballot, Schulze } from "condorcet";

const candidates: Set<Candidate> = new Set(["A", "B", "C", "D", "E"]);

//Build the ballot
const b: Ballot = new Map([
    ["A", 1],
    ["C", 2],
    ["B", 3],
    ["E", 4],
    ["D", 5]

]);

//Construct the Schulze object with the list of candidates
const s = new Schulze(candidates);

//Assume 50 people all voted the same way
s.addBallot(b, 50);

//Get the rankings
ranked: Candidate[] = s.rank();

//Because everybody voted unanimously, you should get the array ['A', 'C', 'B', 'E', 'D'].
//See the tests for more examples.

Ranked Pairs

A description of the method can be found on Wikipedia.

import { Candidate, Ballot, Schulze } from "condorcet";

const candidates: Set<Candidate> = new Set(["Memphis", "Nashville", "Chattanooga", "Knoxville"]);

const b: Ballot = new Map([
    ["Chattanooga", 1],
    ["Knoxville", 2],
    ["Nashville", 3],
    ["Memphis", 4]
]);

const s = new RankedPair(candidates);
s.AddBallot(b1, 42);
const ranked: Candidate[] = s.rank();

//Because everybody voted unanimously, you should get the array ["Chattanooga", "Knoxville", "Nashville", "Memphis"].
//See the tests for more examples.

TODO

• I'm an amateur programmer. Any suggestions to improve efficiency or readability would be warmly welcomed.
• I'm always looking for more test cases. I need to add code for ties.